Static and Dynamic Scoping

The scope of a variable x is the region of the program in which uses of x refers to its declaration. One of the basic reasons of scoping is to keep variables in different parts of program distinct from one another.

Scoping is generally divided into two classes:
1.Static Scoping
2.Dynamic Scoping

Static Scoping:

Static scoping is also called lexical scoping. In this scoping a variable always refers to its top level environment. This is a property of the program text and unrelated to the run time call stack. Static scoping also makes it much easier to make a modular code as programmer can figure out the scope just by looking at the code. In contrast, dynamic scope requires the programmer to anticipate all possible dynamic contexts.

Dynamic Scoping:

With dynamic scope, a global identifier refers to the identifier associated with the most recent environment, and is uncommon in modern languages. In technical terms, this means that each identifier has a global stack of bindings and the occurrence of a identifier is searched in the most recent binding.

A perl code to demonstrate dynamic scoping

$x = 10;

sub f 

{ 

   return $x; 

}

sub g 

{ 

   # Since local is used, x uses

   # dynamic scoping. 

   local $x = 20; 

  

   return f(); 

}

print g()."\n";

Static Vs Dynamic Scoping

In most of the programming languages static scoping is dominant. This is simply because in static scoping it’s easy to reason about and understand just by looking at code. We can see what variables are in the scope just by looking at the text in the editor.

Dynamic scoping does not care how the code is written, but instead how it executes. Each time a new function is executed, a new scope is pushed onto the stack.

Perl supports both dynamic and static scoping.